Architecture of MIA metabolism

EA2106 Architecture of MIA metabolism

Monoterpene Indole alakoids originate from complex biosynthetic pathways exhibiting both thighly regulation processes and high degrees of organisationÂ in planta. Over the last years, the EA2106 research team has engaged (1) program of MIA biosynthetic gene identification as well as (2) the in depth characterization of MIA and terpene biosynthetic pathway compartmentalization at the cellular and subcellular levels focusing on the medicinal plantÂ Catharanthus roseus

For instance, the combined analysis of the cellular distribution of gene transcripts by RNAÂ in situÂ hybridization and proteins by immunological approaches leds to the identification of al least four distinct cells types housing theÂ C. roseusÂ MIA biosynthetic pathwayÂ in folio: (1) cells of the internal phloem associated parenchyma for the early steps of the pathway and notably the methylerythritol pathway, (2) cells of both adaxial and abaxial leaf epidermis for the central steps, (3) the specialized cells idioblasts and laticifers for the final steps of MIA biosynthesis. Such original comparmentalization raises therefore questions about the involvement of metabolite transport in the whole MIA biosynthesis regulation.

(1) Early steps

(2) Intermediate Steps

(3) Final Steps

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An integrated model of the MIA biosynthetic pathway organisation is currently developed by studying the enzyme subcellular localization using GFP imaging and immunological approaches. This notably points out the physical sequestration of the strictosine synthase (STR) in the vacuole and of the stricosidine glucosidase (SGD) in the nucleus engendering a plant defensive mechanism called â€śnuclear time bombâ€ť as illustrated below. Such studies also enable us to establish that peroxisomes play fondamental roles in terpenoid biosynthesis by housing the last enzymes of the mevalonate pathway.Â